1. Field of the Invention
The present invention relates to a headphone and an earphone attached to a user's ear to reproduce sound, and specifically relates to a headphone including a housing defining a back chamber on a back side of a speaker unit.
2. Description of the Related Art
Headphones each include a speaker unit, a housing surrounding a back side of the speaker unit, and an ear contact portion provided on a front side of the speaker unit. The headphones described herein include not only headphones configured such that a pair of right and left housings is coupled through a headband etc., but also earphone type headphones configured such that housings are directly supported on user's ears and a so-called headset configured such that a housing includes a microphone device.
Headphones configured such that a hole is formed at each housing to allow communication between a space in the housing and the exterior have been known as the above-described types of headphones. JP-A-7-170591 describes that for the purpose of improving response in a low sound range by a change in an acoustic equivalent circuit on a back side of an acoustic transducer (a speaker unit) without a change in an acoustic transducer structure, a housing attached to the acoustic transducer includes a duct portion for emitting, to the exterior, sound output from a back surface of the acoustic transducer.
In a case where the hole is, in each headphone, formed at the housing surrounding the back side of the speaker unit such that the space in the housing and the exterior communicate with each other, external noise tends to enter the space in the housing. The noise having entered the housing passes through a speaker unit component exhibiting air permeability, such as a diaphragm or an acoustic filter, and then, reaches a listener's ear. In this case, a listener hears not only the sound output from the speaker unit, but also the external noise. For this reason, there is a problem that the listener cannot clearly hear the reproduced sound of the speaker unit.
Japanese Patent No. 5902202 describes the following headphones as one example of challenges for solving the above-described problem: for, e.g., a purpose that a listener can hear less external noise in the case of allowing communication between the exterior and a space in each housing surrounding a back side of a speaker unit, an internal space and an air chamber formed separately from the internal space are provided in the housing; a space on the inside of an ear contact portion communicates with the inside of the ear of the listener, and communicates with the exterior through the air chamber and the internal space; the air chamber is formed by opposing outer and inner peripheral wall portions of the housing; the outer peripheral wall portion is provided with first holes communicating with the exterior; the inner peripheral wall portion is provided with second holes communicating with the internal space of the housing; and the first and second holes are at different positions along an outer peripheral portion of the housing with the first and second holes not facing each other.
However, in the headphones of Japanese Patent No. 5902202, the second holes (a reference number 35 of FIG. 3) formed at the inner peripheral wall portion of the housing 2 cannot form holes longer than the thickness dimension of an inner wall portion 32, leading to a problem that there is a limitation on acoustic property designing. Moreover, the second holes are formed in such a manner that a coupling member and a housing member are coupled together, each of the coupling member and the housing member being partially recessed corresponding to the holes. Thus, the positions of the facing recesses might shift from each other due to problems on dimension accuracy of components forming the housing and assembly dimension accuracy of the housing. This leads to a problem that the opening dimension and length of the second hole is less stable. As a result, there is a problem that it is difficult for headphones to exhibit excellent reproduced sound quality and stable quality.